1. Field of the Invention
The present invention relates to a preparation method for magnetic fluid, especially to oil-based magnetic fluid that absorbs organic material, oil-based material and metal ions inside the fluid. Then by the application of the magnetic field, the absorbed material is separated from the fluid so as to achieve the purposes of fluid treatment or purification.
2. Description of the Related Art
Magnetic materials have been applied broadly to recording tapes, magnetic materials for memory such as magnetic disks or tapes, building materials such as ink, paint, and mechanical parts such as electromagnetic switches, or seals. By the development of new preparation method, magnetic materials are applied in more fields such as biomedicine for purification of drugs, protein and DNA or environmental waste treatment.
For example, U.S. Pat. No. 4,687,748 applied in 1987 discloses magnetically responsive spheres having an average diameter less than 1,000 nm, prepared by dissolving a carbohydrate polymer in a polar solvent and being applied to cell separation as well as affinity purification. Basically, such magnetic separation techniques have two types according to features of material being processed (1) apply the magnetic field to separate material itself with magnetic properties. (2) combine material without magnetic properties with magnetic material by chemical reactions and then apply the magnetic field for separation. In combination of the material without magnetic properties with magnetic material, various types and preparation methods of magnetic material play important roles.
There are various preparation methods for magnetic material according to users' requirement. The most common is (1) grinding: refer to U.S. Pat. 4,604,222, applied in 1986, magnetic fluid is prepared by mixing of magnetic particles, dispersing agent such as a cationic surfactant and organic liquid carrier such as an ester or a glycol and then employing a grinding or ball mill technique so as to improve electrical conductivity and seal computer disc drives. (2) oxidation reaction: such as U.S. Pat. No. 6,140,001, applied in 2000, disclosing a method that mix a solution of a soluble phosphate compound such as sodium orthophosphate with a solution of ferrous ion, and alkali or alkaline hydroxide solution to form ferrous hydroxide. Then an oxidation step is performed by passing an oxygen-containing gas through the mixture. Finally, the iron oxide particles of the invention will precipitate from the solution. (3) chemical coprecipitation: refer to U.S. Pat. No. 6,743,371, applied in 2004, disclosing magnetic fluid prepared by mixture of magnetic sensitive particles such as nickel-zinc ferrite or manganese-zinc ferrite and conductive particles such as gold, silver, copper, aluminum and graphite. The magnetic fluid is utilized in electrical switching applications. Because the magnetic particles attract each other and thus aggregate, it is necessary to take surface treatment step during preparation process for effectively separation of particles. Not only the diameter of particles is smaller, but the particles are more easily to be dispersed inside the solvent. The ways of surface treatment are different depending on hydrophilic or lipophilic characteristics of the oil-based magnetic fluid being prepared.
As to the preparation of lipophilic oil-based magnetic fluid, refer to U.S. Pat. No. 5,124,060, applied in 1992, a method includes steps of adding the low boiling organic solvent and the dispersant having oleophilic groups to separate particles and heating the resulting material to evaporate the low boiling organic solvent thereby obtaining a magnetic fluid that is applied to seal vacuum apparatus. Moreover, U.S. Pat. 6,068,785, applied in 2000, disclosing a slurry is formed of particles of a non-magnetic oxide of iron (.alpha.-Fe.sub.2 O.sub.3), an oil carrier liquid and a surfactant. The slurry is then processed in an attrition mill to generate magnetic iron oxide particles for form an oil-based material. Due to direct grinding operation, oil and surfactant may attach on surface of magnetic particles so as to make the surface coating fall off. This leads to negative effect on yield rate.
Generally, magnetic fluid is more applied to magnetic materials for memory and design of mechanical seal. However, it's seldom used in eliminating organic compounds or oil inside the water and processing metal ions inside the inorganic wastewater. Conventionally, organic wastewater is processed by heat treating or chemically oxidation. This not only costs much but also generates secondary wastewater due to addition of chemicals. As to wastewater with metal ions, besides conventional chemical precipitation, physical treatment methods such as membrane technologies can also be used. Although there is no addition of chemicals, it requires higher equipment cost and more technical support.
In order to make the oil-based magnetic fluid have lipophilic interface and strong binding force between the magnetic metal oxide particles, the present invention adds surfactant with a carboxyl group during the preparation process of iron oxide so as to generate the magnetic material such as iron oxide with the carboxyl group. Then, the material further reacts with oil material to form oil-based magnetic fluid by crosslinking reaction. The bonding between the magnetic material and the compounds is formed by chemical reaction. Thus the final product has higher bonding force between molecules with better stability.
Thus the oil-based magnetic fluid in accordance with the present invention can react with oils, organic compounds, and metal ions inside water and then being separated by the application of magnetic field. The present invention has advantages of no addition of chemicals, simple equipment and easy operation.